The invention relates to an anti-corrosion agent for use with reinforced cementitious compositions.
More precisely, the invention relates to a method of suppressing the corrosion of steel materials such as reinforcing bars, steel frames and PC steel wires in a concrete structure.
Currently, corrosion inhibition of reinforcing bars or steel frames is achieved by the addition to mortar or concrete of anti-corrosion agents such as nitrites (see JP, B, H2-28532) or alkanolamines (see JP, A, H7-173650), calcium nitrite being particularly effective. Because cementitious compositions such as mortar or concrete contain water, water-soluble anti-corrosion agents are often used.
The problem with water-soluble materials is that, on exposure of a cement product, a concrete product or a reinforced concrete structure containing such agents to wind and rain, water gradually permeates the material and the added anti-corrosion agents are gradually leached out. As a result, the initial corrosion resistance performance decreases over time. Moreover, as nitrites can accelerate concrete setting, it is necessary to adjust for this by also using a retarding agent, especially in hot weather.
Thus, the object of the invention is to provide an anti-corrosion agent for use with a reinforced cementitious composition which solves the abovementioned problems without having an adverse effect on the cement setting or strength, and whose anti-corrosion performance does not diminish prematurely with time.
It has now been found that, although alkyldiamines and alkylamines are slightly soluble in water, they quite unexpectedly demonstrate excellent anti-corrosion properties in a cementitious composition.
Accordingly, the invention provides a method of preventing corrosion of steel reinforcing elements in cementitious structures, comprising the addition to a cementitious mix which will form the structure of an anti-corrosion agent which consists of at least one species selected from a group consisting of alkyldiamines represented by the general formula RHNxe2x80x94(CH)n-NH2 (in which R is an allyl having C8-22 atoms, and n is an integer of 1-5) and alkylamines represented by the general formula Rxe2x80x94NH2 (in which R is an alkyl having C8-22 atoms).
The method not only gives excellent anti-corrosion performance, but also results in low toxicity and does not have an adverse effect on cement setting or strength; therefore, it is easy to handle. Furthermore, as alkyldiamines and alkylamines are basically hydrophobic, they do not leach out even on the exposure to rainfall and do not lose their anti-corrosion effect over time to the same extent as do known anti-corrosion agents.
By xe2x80x9calkyldiaminesxe2x80x9d and xe2x80x9calkylaminesxe2x80x9d is meant not only the compounds themselves but also their salts with inorganic or organic acids. The inorganic acid may be, for example, nitrous acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, pyrophosphoric acid or phosphonic acid. The organic acid may be, for example, formic acid, acetic acid, benzoic acid, citric acid, adipic acid, lactic acid, gluconic acid, heptonic acid, ascorbic acid, sulfanilic acid or salicylic acid. It is possible to use both an alkyldiamine/alkylamine and a salt of one or both compounds in the same anti-corrosion agents.
The anti-corrosion agents used in the present invention may also contain known anti-corrosion agents such as nitrites, chromates, phosphate, benzotriazoles or alkanolamines. Suitable alkanolamines include N,N-diethyl-ethanolamine, N-methyl-ethanolamine, monoethanloamine, diethanloamine, triethanloamine and the like.
Cementitious compositions in which the method of the present invention may be used include cement milk, grout, mortar, concrete or the like which contain at least cement. They are not necessarily mixed with water and can be a dry-mix for the preparation of cement milk, grout, mortar or concrete. Suitable cements include normal cement, high-early-strength cement, moderate heat cement, ultra-rapid-hardening cement, blast furnace slag cement, fly ash cement and the like.
The method of the present invention may be performed by adding the anti-corrosion agent to a cementitious mix such as cement milk, grout, mortar or concrete in a range of 0.05-5.0 wt. % on the basis of the cement weight in the cementitious composition.
Additionally, the anti-corrosion agents for the cementitious compositions of the method of the present invention may be used together with other known additives for mortar or concrete, including water-reducing agents, air-entraining agents, setting accelerators, retarders, expansive agents, plastic emulsions, and so on.
The invention further provides a reinforced cementitious structure comprising a hard cementitious composition which has within it steel reinforcing members, the reinforcing members being protected from corrosion by the incorporation in the cementitious composition prior to hardening of an anti-corrosion agent which consists of at least one species selected from a group consisting of alkyldiamines represented by the general formula RHNxe2x80x94(CH2)n-NH2 (in which R is an alkyl having C8-22 atoms, and n is an integer of 1-5) and alkylamines represented by the general formula Rxe2x80x94NH2 (in which R is an alkyl having C8-22 atoms).